Operator Overloading

1. Operator Overloading

2. Outline • Revision • What is Operator Overloading • Why Operator Overloading • Overloading Unary operators • Overloading Binary operators • Overloading Assignment operator

3. Revision • Operator Overloading is a mechanism to redefine built-in operations for user defined types • It allows to give normal C++ operators such as +,-,==,< additional meanings • Operator Overloading should be used to perform the same function or similar function on class objects as the built-in behavior

4. Revision • Operator overloading is a very neat feature of object oriented programming in C++ • Each individual operator must be overloaded for use with user defined types • Overloading the assignment operator and the subtraction operator does not overload the -= operator.

5. Things to keep in mind • At least one of the operands in any overloaded operator must be a user-defined type • operator + for one integer and one double, NOT possible • Can only overload the operators that exist. • All operators keep their current precedence and associativity, regardless of what they're used for

6. Operator Functions • Operator functions may be defined as either member functions or as non-member functions. • Non-member functions are usually made friends for performance reasons. • Member functions usually use the this pointer implicitly.

7. Commonly Overloaded Operators • Unary • ++, --, (increment, decrement) • Binary • +, -, *, /, % (arithmetic) • =, +=, -=, *=, /=, %= (assignment) • ==, !=, >, <, >=, <= (relational) • <<, >> (I/O) • ||, && (logical) • &, |, ^, ^=, &=, |= (bitwise)

8. Non-overloadable Operators • . (dot operator / member selector) • :: (scope resolution operator) • ?: (conditional operator / arithematic if) • .* (member pointer selector) • sizeof

9. Overloading Unary Operator • Increment Operators ( ++) • Unary Operators ( --)

10. Example • #include <iostream> • using namespace std; • //////////////////////////////////////////////////////////////// • class Counter • { • private: • unsigned int count; //count • public: • Counter() : count(0) //constructor • { } • unsigned int get_count() //return count • { return count; } • void operator ++ () //increment (prefix) • { • ++count; • } • };

11. int main() • { • Counter c1, c2; //define and initialize • cout << “\nc1=” << c1.get_count(); //display • cout << “\nc2=” << c2.get_count(); • ++c1; //increment c1 • ++c2; //increment c2 • ++c2; //increment c2 • cout << “\nc1=” << c1.get_count(); //display again • cout << “\nc2=” << c2.get_count() << endl; • return 0; • }

12. Overloading Binary Operators • Arithmetic Operators • Assignment Operators • Comparison Operators • Arithmetic Assignment Operators